In recent progress of barrier-free items, easy opening is considered to be an important function for wrapping films. Typical methods for making the wrapping bags easily openable include a method of providing the wrapping bags with cutting-start points such as V-shaped notches, etc. in their edge portions (heat-sealing portions), and methods needing no cutting-start points such as a magic cut method, a fancy cut method and a method of providing the wrapping bags with fine pores.
The magic cut and the fancy cut comprise providing the wrapping bags with fine scratches in their edge portions and bending portions in place of notches. However, even with the magic cut or the fancy cut, it has been difficult to open the wrapping bags straight in directions not aligned with the molecular orientation of plastic films. Further, when cut lines progress in conventional easy-to-open wrapping bags beyond their edge portions to regions in which contents are included, the cut lines are likely to unintentionally go toward the regions having contents even though plastic films for the bags have molecular orientation, resulting in falling, dropping or scattering of the contents.
Working for making a plastic film porous (porous working) is to form a lot of fine penetrating or non-penetrating pores on the entire surface of the film. Thus, wrapping bags of films subjected to the porous working can be opened from any position without notches regardless of the directions of the films. Accordingly, even if an opening operation is temporarily stopped, the bags can be opened to the end. However, because films for wrapping food, etc. are required to have moistureproofness, the film subjected to the porous working should be laminated as an outermost film.
JP 2002-80705 A discloses an easy-to-tear, biaxially stretched polyester film, which can be easily torn straight. However, when used for applications of wrapping films requiring moistureproofness, the biaxially stretched polyester films should not be used alone but laminated with polyolefin films, etc., to provide wrapping films.
Vapor-deposited transparent films are widely used as gas-barrier films to wrap food, medicine, high-precision electronic parts, etc. However, because the vapor-deposited transparent films are composed of thermoplastic resin films vapor-deposited with metals, metal oxides, etc. and coated with resins, they have insufficient easy-to-tear characteristics even though the plastic base films have easy-to-tear characteristics.
For instance, cut tapes are attached to wrapping films for triangular rice balls sold at convenience stores and the like to enable cutting in a strip shape. To adhere the cut tapes to the films, transfer methods are usually used. As a result, the films cannot be moved at a high speed in the production of the wrapping films, resulting in low productivity and high production cost.